In staplers, a staple driver forces a staple to penetrate a group of papers supported on an anvil, the legs of the staple finally being set by the anvil against the back of the papers. This operation is performed almost universally in staplers currently available by a staple driver that is itself driven by force transmitted from the user's hand. These may be called "manual-drive" staplers.
Hesitation and relaxation of effort by the user of a manual-drive stapler results in retraction of the staple driver. Similar effects occur when a stapler is just "slapped" without enough effort to advance and curl the legs of the staple against the anvil. Under such conditions, another staple tends to be advanced partially into driving position, and when the stapler is operated again, it tends to become jammed.
Some manual staplers have been equipped with stroke-completion mechanisms. Those mechanisms are intended to block return motion of the staple driver even if the user's effort is relaxed before the staple-driving stroke is completed. Such mechanisms increase the cost of the staplers, and the stroke-completion mechanism is itself an occasional cause of jamming. Consequently, most staplers on the market are not equipped with stroke-completion mechanisms.
Electrically operated staplers avoid the problems related to hesitation by the user for, once the operating switch is closed, the stapler ordinarily operates in its prescribed stroke. The electric stapler is designed to provide ample effort to complete its stroke under all normal circumstances, taking into account the sharpness of standardized staples and the toughness and maximum number of sheets to be stapled together. However, electric staplers are costly and massive so that manual staplers are vastly more common.
Staples are also used in tackers, where the staple is driven into a thick object, as in tacking a poster to a wooden post. Manually-operated tackers commonly use a staple driver that is powered by a spring. During most of the stroke a manual operating lever compresses the spring, and the staple driver is released over the end of the operating stroke to drive the staple into the work. There is no anvil nor any need for an anvil.